Braun tube



' sept. 6, 193s. V E. HUDEC 2,125,065

BRAUN TUBEl Filed March 2e, 1954 Patented Sept. 6, 1938 PATENT FFiCEBRAUN TUBE Erich Hudec,

Application March 26,

Berlin, Germany 1934,r Serial No. 717,296

In Germany April 8, 1933 Claims.

' It is well known to apply Braun tubes to the purposes of television byproducing between the anode and the deecting plates a rejection chamberwhich is closed against the deflection space by a diaphragm with anopening of, the diameter of the cathode ray, and in which the cathoderay is defiected by electro-static or magnetic iields in jsuch mannerthat neither the ray itself nor diffused stray electrons are able toenter the defleclO tion space and in that way to reach the screen of theBraun tube. The fields within the rejection chamber are either Zero sothat the cathode ray is allowed to pass unexerted through the diaphragmor they possess such a value that the cathode ray is completely stopped.With this arrangement it is therefore only possible to produceblack-white pictures, while the grey intensity Values can not at all bereproduced.

In the art of television it is however indispensable to reproduce allhalf-tone values of the picture. This may be accomplished in principalfashion by Varying the potential of. a grid electrode arranged near thecathode (e. g. a Wehnelt cylinder surrounding the cathode). In allpractical experiments which have been undergone up to now it has beenstated that besides a desired variation of the intensity of thefluorescent image point an undesired variation of the position of thepoint takes place by which the television image is very stronglydistorted.

The invention is based on the theory that the variation in the positionof the image point is stipulated by asymmetry. In case the heaterelement is lying not exactly on the axis of the Wehnelt cylinder and theanode, the electrons are accelerated in lateral fashion. The degree ofthe lateral deflection is determined by the geometrical dimension and bythe voltages between the Wehnelt cylinder and the cathode. Upon varyingthis voltage for the variation of light intensity of the fluorescentpoint the acceleration of the electrons is Varied, the electrons arelightening the screen in another spot.

The disturbing shifting the image point in the 45 case of Braun tubeswith intensity control according to the invention is removed bysupporting all electrodes by the aid of a precise gauge, whichafterwards upon fixing the electrodes by melting them to the supportsmay easily be removed 50 without damaging the electrodes.

One object of theinvention is a Braun tube for television purposescomprising a thermionic cathode, a control electrode arranged in theproximity of said cathode, and an anode arranged in operativerelationship to said cathode, and

(Cl. Z50-27.5)

wherein the emissive surface of said cathode is exactly aligned with theaxis of said control electrode and with the axis of said anode.

A further object of the present invention is a simple method forproducing Braun tubes of this kind. Still further objects of. theinvention will be seen from the following description.

The invention may be more fully understood with reference to theaccompanying drawing in which Fig. 1 shows by way of example anarrangement Vfor mounting the electrodes of the Braun tube in preciselycentered fashion, and Fig. 2 shows an exemplary form of a gauge.

In Fig. l, l is the heater element for instance a filament which issup-ported by two leads which are melted to the press l. All the otherelectrodes, the Wehnelt cylinder 2, and anode 3 and the deflectionplates 4 and 5 are fastened to two glass rods 6 which are melted withthe press i and serve as a support.

As basic element of the gauge according to the Fig. 2 a cylindrical rod8 is provided which is either guided by two electrodes or better in aspecial rack independent of the assemblage of electrodes. On thiscentering rod there are arranged distance pieces 9, I D, l l by whichpieces an exactly symmetrical position of the several electrodes isguaranteed. After the several electrcdes having been melted to the glassrods the centering rod and the distance pieces are carefully removed. Inorder to avoid a damage of the structure the distance pieces may beconstructed of two parts and allowed to be opened.

By tensioning the gauge in a frame, which is mounted between two points,it is possible, after removal of the gauge, to examine mechanicallywhether the electrodes are still exactly centered. For this purpose thegauge frame is rotated between the two points, and a check taken whetherthe rotary members still run, Since the eye responds very well to slightknocking on the part of rotary members, the accuracy of this test isvery considerable.

In carrying out this method it has been found that the singleelectrodes, which were centered in the gauge with considerableexactitude, did not run cleanly after the removal of the gauge, andrequired slight subsequent adjustment.

The distortion of the electrodes is due to stresses in the glass. Todiminish these stresses the two glass rods, after al1 electrodes hadbeen fused in, were again .greatly heated over their entire length andthen slowly cooled. The stresses, however,Y were not in this wayeliminated.

The invention is based on the recognition that the stresses in the glassare due to the extensive heating of the metallic attachment wires of theelectrodes. These wires require to be greatly heated when fused into theglass rods. After cooling the wires contract, and produce theundesirable stresses. Subsequent heating of the holding rods is oflittle value, as in this way the attachment wires are also heated andcontact anew when allowed to cool.

The objections associated with the known method are avoided according tothe invention by fitting on the electrodes short glass rods, which arefused to the holding rods. The advantage of this method consists in thefact that when fusing glass to glass a considerably smaller heating isrequired, and that the glass may be heated locally, whereas otherwisethe metallic connecting wires are also heated over their entire lengthand contract over their entire length when allowed to cool.

To the electrodes, for the purpose of their attachment, there are Weldedmerely Very short metallic rods composed of a suitable fusing wire, andon to these there are fused short thin glass rods. The electrodes arethen assembled in the gauge, and finally the holding rods are fused tothe glass rods. Preferably at first the outermost deflecting plate isfused to the glass rods, so that the same is furnished with a hold andis unable to flex.

In order that the fusing of the glass rods may take place as quickly aspossible and the gauge not heated excessively, it is desirable to employa glass having the lowest possible fusing point, for example lead glass.

I claim:

l. A Braun tube for television purposes comprising a pinch, twoinsulating rods secured to said pinch, a thermionic cathode having anemissive surface and being secured to said pinch, a control electrode,and an anode arranged in operative relationship to said cathode, saidcontrol electrode and said anode being each secured to, and located inexact axial alignment with respect to said emissive surface by, said twoinsulating rods.

2. A Braun tube for television purposes comprising a pinch, two glassrods secured to said pinch, a thermionic cathode having an emissivesurface and being secured to said pinch, a control electrode, and ananode arranged in operative relationship to said cathode, said controlelectrode and said anode being each secured to, and located in exactaxial alignment with respect to said emissive surface by, said two glassrods.

V3. A Braun tube for television purposes comprising a pinch, twoinsulating rods secured to said pinch, a thermionic cathode having anemissive surface and being secured to said pinch, a control electrode,an anode arranged in operative relationship to said cathode, and adeflecting electrodes system, said control electrode, said anode, andsaid deflecting electrodes system being each secured to, and located inexact axial alignment with respect to said emissive surface by, said twoinsulating rods.

4. A Braun tube for television purposes comprising a pinch, glass rodsfused to said pinch, a thermionic cathode having an emissive surface andbeing secured to said pinch, a` control electrode, and an anode arrangedin operative relationship to said cathode, at least one short glass rodsecured to said control electrode and to said anode, each, said shortglass rods being fused to said glass rods fused to said pinch to securesaid control electrode and said anode each to said two glass rods fusedto said pinch and so to locate said control electrode and said anode inexact' axial alignment with respect to said emissive surface.

5. A Braun tube for television purposes comprising a pinch, glass rodsfused to said pinch, a thermionic cathode having an emissive surface andbeing secured to said pinch, a control electrode, an anode arranged inoperative relationship to said cathode, and a deflecting electrodessystem, at least one short glass rod secured to said control electrode,to said anode, and to said deflecting electrodes, each, said short glassrods being fused to said glass rods fused to said pinch to secure saidcontrol electrodes, said anode, and said deilecting electrodes systemeach to said two glass rods fused to said pinch and so to locate saidcontrol electrode, said anode, and said deflecting electrodes system inexact axial alignment with respect to said emissive surface.

ERICH HUDEC.

